convert bgra to png complains of no file, but file exists

[DDR]

Hello. I'm trying to convert a raw bgra-formatted image to a png on Ubuntu.

The natural command to try is

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convert -size 800x480 -depth 8 /tmp/screenshot.bgra /tmp/screenshot.png

but this does not work, claiming

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convert-im6.q16: unexpected end-of-file `/tmp/screenshot.rgba': No such file or directory @ error/rgb.c/ReadRGBImage/243.
convert-im6.q16: no images defined `/tmp/screenshot.png' @ error/convert.c/ConvertImageCommand/3258.

Running identify yields the same rather unhelpful error.

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$ identify -size 800x480 -depth 8 /tmp/screenshot.bgra
identify-im6.q16: unexpected end-of-file `/tmp/screenshot.bgra': No such file or directory @ error/bgr.c/ReadBGRImage/244.

Now, at this point, I know you're thinking I'm a fool who couldn't find his image if it were in the directory in front of him. However,

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$ ls -la /tmp/screenshot.bgra
-rw-rw-r-- 1 david david 25165824 Sep 18 16:00 /tmp/screenshot.bgra

says it is there, and it's full of data, and it imports into Gimp just fine if I rename it to screenshot.data.

If I run

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convert -size 800x4 -depth 8 /tmp/screenshot.bgra /tmp/screenshot.png

then I get several hundred very short .png images, which isn't what I expected at all. I think I've missed something fairly fundamental, but I don't know where.

I have uploaded the sample input and output to https://filebin.net/e1bbejly48gmktnn/sc ... t=fdwiigio, which should be valid until 2019-09-14.

Thank you.

[snibgo]

What is in your screenshot.bgra? You suggest it has 800x480 pixels, with 4 channels, 1 byte/channel/pixel. So that would be 1536000 bytes. But your file is much larger at 25 MB.

EDIT: This works without complaint:

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magick -size 4096x1536 -depth 8 screenshot.bgra x.png

The result looks bad because I probably mis-guessed the actual dimensions.

[DDR]

Hm, upon further investigation, it seems what I was getting out of my source - "cat /dev/fb0" - was an 800xlots image, not the 800x480 image I was expecting. The first 800x480 pixels were good - which was why Gimp could open them - but the rest was garbage which was confusing ImageMagick. I've amended the source command to "cat /dev/fb0 | head --bytes=1536000" which works fine.

Thank you for your help, snibgo.

[snibgo]

Yes, that works:

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head --bytes=1536000 screenshot.bgra | magick -size 800x480 -depth 8 BGRA:- out.png